The purpose of this paper is to discuss the use of various completion fluids for petroleum production. A number of completion fluids have been around for some time, but, for the most part, are inadequate for use lithe deeper, higher pressure wells.
During well completion and walkovers, fluid movement in the well bore. should be kept to a nimbus. This is accomplished by introducing fluid into the well that is dense enough to control the reservoir pressure. In most cases, all that is necessary is to equalize the pressure of the formations. However, for greater safety and to aid certain completion techniques, a differential positive pressure into the formation is required.
Being able to maintain a positive pressure into the formation depends upon the reservoir pressure and the density of the fluid used to control it. The higher the reservoir pressure, the greater the density required.
Solutions of sodium chloride, calcium chloride and zinc chloride, and slurries of calcium carbonate and other solids have been used in an attempt to obtain the needed densities. Salt water has also been used. It is extremely economical, but it is limited to about 10 bagel maximum density. Calcium chloride is satisfactory to about 11.6 Ib/gal. Calcium carbonate has limited solubility in water. And in order to obtain higher densities, other insoluble?s are used.
The insoluble?s can present some serious problems as suspended solids can be detrimental in well completions. Both laboratory and field tests indicate that permeability can be reduced or destroyed by perforating or working in fluids containing suspended solids. Often gas or oil production is difficult, and sometimes impossible, to regain.
Commonly used drilling mud use insoluble solids as weighting materials. During perforating, sand consolidation operations, or other completion procedures, these materials are exposed to the formation; and frequently, some of the fluid in the well bore is injected or lost to the formation. The suspended solids are filtered by the reservoir matrix. This operation can and has decreased the perms ability, and in some cases wells have beenplugged and valuable production has been lost. Another old timer, zinc chloride, has numerous shortcomings. It is highly corrosive, environmentally degrading, and is known to bio-concentrate in shell fish. This last characteristic of zinc can be especially damaging when used in the Gulf Coast area. Zinc also has a short shelf life.